Adds an rmcp-based stdio MCP client in harness-mcp plus adapters exposing a configured server's tools as namespaced harness-tools, with an echo-server fixture and integration test, and wiring through harness-app.
Sets up the Cargo workspace (harness-core, harness-tools, harness-providers, harness-mcp, harness-lsp, harness-app, harness-tui) and the ten architecture docs under docs/. harness-core gets its foundational types (session/message/part/model ids), an in-process event bus, a table-driven permission evaluate function, and a SQLite-backed storage actor with schema and roundtrip coverage. Every crate compiles empty and a bin stub prints its version.
darman